1. Field of the Invention
The present invention relates to a method of determining a principal portion of an image and a method of determining a copying condition, and more particularly to a method of determining a principal portion for determining a region having a high probability of being a region corresponding to a principal portion of an image, as well as a method of determining a copying condition in such a manner as to allow a principal portion of an image to be copied appropriately.
2. Description of the Related Art
In the appreciation of photographs, viewers' attention is mostly focused on a particular portion (hereafter referred to as a principal portion) of the image just as the face of a human figure attracts the greatest attention in the case of portraits, for example. Therefore, when an original image recorded on a recording material such as a film is copied onto a copying material such as a photographic printing paper, it is necessary to determine a copying condition in such a manner that the principal portion, such as the face of a human figure, is printed appropriately.
For this reason, in Japanese Patent Application Laid-Open No. 346332/1992, the applicant proposed a technique wherein a color original image is divided into a multiplicity of pixels, and is spectrally separated into three colors and photometrically measured for each pixel; a histogram on hue values (and saturation values) is determined on the basis of data obtained by the photometry; the determined histogram is divided into ridges; a determination is made as to to which of the divided ridges each pixel belongs, and each pixel is classified into groups corresponding to the divided ridges; the color original image is divided into a plurality of regions for each group; a region corresponding to the face of a human figure serving as the principal portion among the plurality of regions is estimated; and the exposure amount is determined on the basis of the photometric data on the estimated region.
With the above-described technique, however, in a case where a non-human figure region of flesh color, such as the ground or a trunk of a tree, which is present in the original image, is located adjacent to the region corresponding to the face of the human figure, it is difficult to separate the region corresponding to the face of the human figure and the non-human figure region.
In addition, in Japanese Patent Application Laid-Open No. 160993/1994, a proposal has been made in which, in the above-described technique, to improve the probability of extracting a region corresponding to the face of a human figure, a region abutting against an outer periphery of the image is determined to be a background region and is eliminated, or an extracted region is represented as a diagram, and a determination is made as to whether or not the extracted region is a region corresponding to the face of a human figure, on the basis of the shape of a neighboring region located in the vicinity of the extracted region or the shape of the extracted region.
With the above-described technique, however, a skin-colored region, such as the ground or a trunk of a tree, is present in the original image, in a case where the hue and the saturation of the skin-colored region are similar to the hue and the saturation of the region corresponding to the face of the human figure in the original image, there is a possibility that this skin-colored region is erroneously determined to be a region corresponding to the face of a human figure. In addition, if this skin-colored region is adjacent to the region corresponding to the face of the human figure, the skin-colored region and the region corresponding to the face of the human figure cannot be separated from each other, so that the region corresponding to the face of the human figure cannot be extracted appropriately.
The problem encountered in the above-described methods is attributable to the fact that the contents of images photographic processing of which is requested are indefinite, and that images of various contents are brought in. Namely, the present situation is such that it is difficult to reliably extract a region corresponding to the principal portion of an image in each of the above-described various methods of extracting a principal portion or the methods of extracting a principal portion proposed by the applicant in Japanese Patent Application Laid-Open Nos. 265850/1994 and 266598/1994. In each method, images whose principal portions are possibly extracted erroneously are present. For instance, a non-principal portion is erroneously extracted as a principal portion, or a region in which a non-principal portion and a principal portion are present in a mixed form is erroneously extracted as the principal portion. Conversely, a principal portion is determined to be the region corresponding to a non-principal portion, and is not extracted.
Accordingly, even if an attempt is made to automatically determine the copying condition (exposure amount) by extracting the principal portions according to any one of the above-described methods, the incidence in which an appropriate copying condition cannot be obtained due to the erroneous extraction of the principal portion occurs with a probability exceeding a predetermined value. Hence, it has been difficult to improve the probability of obtaining an appropriate exposure amount.